Primuladongchuanensis (Primulaceae), a new species from northern Yunnan, China

Abstract Primuladongchuanensis Z.K.Wu & Yuan Huang, a new species of Primulaceae from Dongchuan of northern Yunnan, China, is described and illustrated. Both morphological and molecular evidence support P.dongchuanensis as a member of the sect. Proliferae. It is similar to P.aurantiaca W.W.Smith & Forrest, but is distinguished by having unique raceme inflorescences. Its distribution, phenology and conservation status are also provided.


Introduction
Primula Linn. is one of the largest genera of Primulaceae, including about 500 species worldwide. Most Primula species are indigenous to the north temperate zone, with only a few outliers on some mountains of Africa (Ethiopia), tropical Asia (Java and Sumatra) and South America (Hu 1994, Hu and Kelso 1996, Mast et al. 2001. The modern center of diversity of Primula is in southwestern China, with ca 300 species of 24 sections, most of which occur in western Sichuan, eastern Xizang, and northwestern Yunnan (Hu 1994, Hu andKelso 1996). Increased exploration across this region results to the discovery and description of new Primula species in the past 15 years (Hu and Geng 2003, Wu et al. 2013, Xu et al. 2017a, 2017b, Yang et al. 2017, Ju et al. 2018 Section Proliferae Pax (10:217, 1889) of the genus Primula comprises more than 20 species, mainly distributed in Eastern Himalaya and Hengduan Mountain in China. Most species in this section are horticulturally important plants. Morphologically, sect. Proliferae shows the distinct character of several whorls of flowers in superimposed umbels and is recognized as a 'natural' group in this genus. Previous studies presumed that the sect. Proliferae may represent the most primitive group of Primula alive today, and take a central position with respect to subsequent evolution and geographical migration in the genus (Richards 1993(Richards , 2002. However, molecular phylogenetic evidence posited the opposite conclusion and indicated that the sect. Proliferae represents relatively advanced members of Primula that exist today (Mast et al. 2001, 2004, Yan et al. 2015. During the field investigation in the Jiaozi Snow Mountain in Dongchuan of Yunnan, southwestern China in 2011, we found a peculiar population of Primula in its vegetative stage on a small patch of alpine meadow near the mountain top. We transplanted some living individuals to Lijiang Alpine Botanical Garden (at elevation of ca. 3200m), northwest of Yunnan and they regained their bloom in subsequent years. The plant has a short rootstock and robust fibrous roots, obovate-oblong to oblanceolate leaves forming a dense rosette and flowers showed great similarity to the species of sect. Proliferae, except the inflorescences with obsolete scapes at early anthesis, then elongating to forming raceme at late flowering. We presumed the unusual inflorescence springs from abnormal variations of plant response to a different climate zone and soil type after translocation. After the field investigations in the same locality in 2016 and in 2019, we confirmed that the inflorescences we observed from the translocated individuals are morphologically consistent with those of the wild population. Further molecular phylogenic analysis revealed it is an undescribed taxon of sect. Proliferae. We concluded that the species is new to science and describe it here.

Materials and methods
Morphological descriptions and comparisons were based on living plants from the Lijiang alpine botanical garden and in the field, specimens from the herbarium of Kunming Institute of Botany, Chinese Academy of Sciences (KUN), and literatures (Chen andHu 1990, Hu andKelso 1996). All morphological characters of P. dongchuanensis and its morphological similar species P. aurantiaca were measured using a vernier caliper. The conservation status of P. dongchuanensis was assessed according to the IUCN Red list Categories and Criteria (IUCN 2017).
Phenology. Flowering occurs from late April to early June; fruiting from July to August.
Distribution and ecology. P. dongchuanensis is only known from the type locality in northern Yunnan, China. The plant has been found on alpine meadow and forest margin at elevation of ca. 3800-4000 m (Fig.2), associated with Sibbaldia purpurea Etymology. The epithet of the new species is derived from the name of Dongchuan in northern Yunnan, where the new species was discovered and collected. Vernacular name. Chinese mandarin: dong chuan bao chun (东川报春) Molecular evidence. The phylogenetic tree obtained from ML analysis is shown in Figure 4. Phylogenetic analysis showed that the new species clustered with other sampled species of sect. Proliferae and together formed monophyletic clade with a strong support (UFBoot value = 100%, SHaLRT value = 100%), which indicates it is a member of sect.
Proliferae, and the tree shows that P. dongchuanensis is well differentiated from its close relatives; this is consistent with its special morphological characters in sect. Proliferae.
Conservation status. Currently, P. dongchuanensis is only known from the top of Jiaozi Snow Mountain in a single population with fewer than 1000 individuals on ca. 2000 m 2 occupancy along the alpine meadow. Although there is no obvious population change observed, the original habitat suffered severely from over-grazing based on three field expeditions conducted in 2011, 2016 and 2019. Living collections introduced to Lijiang alpine botanical garden in 2011 were able to flower and set seeds in the following two years, but no individuals were flowering after the fourth year. Other ex-situ conservation actions, such as seed banking, may apply to secure conservation of this unique Primula species. According to the guideline of IUCN red list criteria (IUCN 2017), this new species is assessed as 'Vulnerable' (VU D1).

Discussion
Sect. Proliferae Pax is a taxonomically well-known group in Primula, characterized by numerous whorls of flowers resembling candelabra (Fig. 3) (Chen and Hu 1990). Phylogenetic analyses by using DNA barcoding confirmed the monophyly of sect. Proliferae which could be used in narrowing the scope of identification in Primula (Yan et al. 2015). Preliminary molecular phylogenetic analyses in this study supports the view that P. dongchuanensis is a member of sect. Proliferae, but its molecular closed relatives are not clear yet. Further research is required to clarify the phylogenetic relationship by using enhanced molecular markers with a wider sampling in this section.
Morphologically P. dongchuanensis has unique inflorescences architecture compared to other members of sect. Proliferae. The racemose inflorescence appears in some Primula species, but no report in the sect. Proliferae till the addition of P. dongchuanensis, which extended the delimitation of sect. Proliferae and increased our knowledge of the Primula diversity in China. Compared to other species of the sect. Proliferae with bigger and upright inflorescences when anthesis begins, P. dongchuanensis keeps the racemes in a condensed and short form. This could flow from adaptation to the harsh habit of the mountain top where it is usually very windy and insufficient water in late April and May when it starts anthesis, and the other species of sect. Proliferae are usually found in the open and wet alpine meadow and have a late bloom time.